The present invention relates to a process for preparing unsaturated heterocyclic compounds containing carbonyl functionality. More particularly, the present process employs an electrochemical oxidation of saturated heterocyclic precursors in solution followed by elimination of the oxidatively added substituent along with adjacent hydrogen to prepare the desired unsaturated functionality.
T. Shono et al., J.A.C.S., 97, 4264 (1975) prepared linear .alpha.-methoxy-substituted urethanes by anodic oxidation of methyl N-alkyl-substituted carbamates in methanol. The compounds were found to demethanolate under acidic or thermolytic conditions, Id., at 4266, column 2, 6th paragraph.
In European Patent No. 9,697, the anodic oxidation of certain carbamates including 2-oxazolidinone in methanol solution to prepare .alpha.-methoxy-substituted urethane derivatives was disclosed, Id., at page 4, line 27. The reference further taught at page 13, line 13 that the .alpha.-methoxy-substituted urethanes prepared may be used as starting material to prepare vinyl urethanes suitable for preparing polymers as disclosed by James T. K. Woo et al., J. Polymer Sci., B, 7, 181 (1969). The latter reference taught the use of a variety of N-vinyl compounds including N-vinyl pyrrolidone in radiation-induced polymerizations.
In U.S. Pat. No. 4,322,271, N-vinyl-N-alkyl carboxylic acid amides were prepared by the anodic oxidation of N-ethyl carboxylic acid amides followed by a splitting off of alcohol functionality. The reference provides a thorough discussion of known techniques of splitting off alcohol functionality for which teaching the above patent is incorporated in its entirety by reference.
Previous methods of preparing unsaturated heterocyclic carbonyl compounds have not proven acceptable for commercial implementation. Hartmann and coworkers, Liebigs Ann. Chem., 1319 (1976), prepared 3-acetyl-2(3H)-oxazolones by the photochlorination of 3-acetyl-2-oxazolidinones in carbon tetrachloride solution, followed by dehydrochlorination of the resulting product. A yield of 50 percent was obtained.
Imidazol-2-ones have been prepared by several techniques. The most common preparation involves the cyclization of an aminoketone or aldehyde derivative with KOCN or HOCN. See, e.g., Duschinsky et al., J.A.C.S., 2350 (1946), or Ger. Offen. No. 2,718,058.
Unsaturated heterocyclic compounds containing carbonyl functionality are useful monomers for polymerization and copolymerization processes, e.g., to prepare polyethyleneamines or poly(1-amino-2-hydroxyethylene) resins and films that have uses in metal chelation, gas conditioning and other applications. Particular compounds are also capable of use in special applications. For example, imidazol-2-ones are known to possess useful bacteriostatic activity and may be converted to 2-imino derivatives of substituted imidazolones that are known plant growth regulators as taught by U.S. Pat. No. 3,887,577. The compounds are further useful as intermediates in the preparation of pharmaceuticals and other fine organics.
Prior methods of anodic oxidation have been concerned with the preparation of .alpha.-alkoxy-substituted compounds and N-vinyl-substituted derivatives thereof. To the best of my present knowledge no attempt has been made to prepare unsaturated heterocyclic carbonyl-containing compounds by an electrochemical oxidation followed by elimination of alcohol or acid groups to prepare cyclic unsaturation.
It would be desirable to provide a process for the preparation of 2H-pyrrol-2-one, 2(3H)-oxazolone and 2H-imidazol-2-one compounds from the corresponding saturated precursors: 2-pyrrolidinone, 2-oxazolidinone and imidazolidine-2-one compounds.
It would further be desirable to provide such a process that avoids the formation of inorganic or organic salt by-products but rather results in the formation of useful by-products under neutral reaction conditions.
Finally, it would be desirable to provide a process that allows the facile recovery of the desired product in high yields and purity.